JP6337397B2 - Power converter and power conditioner using the same - Google Patents

Description

  The present invention generally relates to a power converter and a power conditioner using the same, and more particularly to a power converter that converts power from a DC power source and a power conditioner using the same.

  In recent years, with the spread of residential solar power generation devices, fuel cells, power storage devices, and the like, various circuits have been proposed and provided as power conversion devices that convert the output of these DC power sources into AC. For example, Patent Documents 1 and 2 disclose a power converter that generates an AC output converted from a DC voltage source into a plurality of voltage levels (“Multi-level power converter” in Patent Document 1 and “Converter Circuit” in Patent Document 2). Is disclosed.

  According to the description of Patent Document 1, the power conversion device is a 5-level inverter that outputs a 5-level voltage, and includes two DC capacitors, two flying capacitors, and 10 switching elements. ing. In this power converter, in the state where the DC voltage E is applied to the series circuit of two DC capacitors, the voltage of each DC capacitor becomes E / 2 and the voltage of each flying capacitor becomes E / 4. By controlling the switching element, a five-level voltage is output.

JP 2014-64431 A (paragraphs [0002] to [0006], FIGS. 16 and 17) Japanese Patent No. 4369425

  By the way, in the conventional power conversion device as described above, in order to maintain the voltage of the capacitor (flying capacitor) at a specified voltage, it is necessary to perform control for switching between charging and discharging of the capacitor. However, since the conventional power conversion device is configured to charge or discharge a pair (two) of capacitors (flying capacitors) at the same time, once the voltage of the pair of capacitors becomes unbalanced, It is difficult to balance the voltage. Therefore, in the conventional power conversion device, the voltage of one pair of capacitors may be unbalanced, and the voltage of one capacitor may exceed the specified voltage. It is necessary to use a withstand voltage capacitor.

  This invention is made | formed in view of the said reason, and it aims at providing the power converter device which can reduce the proof pressure requested | required of a capacitor, and a power conditioner using the same.

  The power conversion device of the present invention includes a first conversion electrically connected in parallel between a first input point on the high potential side of a DC power supply and a second input point on the low potential side of the DC power supply. A first switching element and a second switching element from the first input point side between the first input point and the second input point. First to fourth switching elements electrically connected in series in the order of the element, the third switching element, and the fourth switching element, and the series circuit of the second switching element and the third switching element And a first capacitor electrically connected in parallel with each other, a connection point between the second switching element and the third switching element as a first output point, and the second conversion circuit includes: The first input point and the second input point Are connected in series in the order of the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element from the first input point side. And a second capacitor electrically connected in parallel with a series circuit of the sixth switching element and the seventh switching element, and the sixth switching element and the seventh switching element. The connection point between the first switching element and the second switching element is the second output point, and the first connection point, the seventh switching element, and the eighth switching element are the connection points of the first switching element and the second switching element. A first bidirectional switch electrically connected to a second connection point, which is a connection point of the third switching element, and the third switching element and the fourth switching point. A second bidirectional switch electrically connected between a third connection point that is a connection point of elements and a fourth connection point that is a connection point of the fifth switching element and the sixth switching element; The DC power source, the first capacitor, and the second capacitor for the first output point and the second output point are controlled by controlling the first to eighth switching elements and the first and second bidirectional switches. And a controller that changes the magnitude of an output voltage generated between the first output point and the second output point in a plurality of stages. When the difference between the voltage of the capacitor and the voltage of the second capacitor exceeds a predetermined threshold, only the higher one of the first capacitor and the second capacitor is discharged. The first to eighth switching elements and the first and second bidirectional switches are controlled.

  A power conditioner according to the present invention includes the power conversion device described above and a disconnector electrically connected between the first output point, the second output point, and a system power supply. .

  The present invention has the advantage that the breakdown voltage required for the capacitor can be lowered.

It is a circuit diagram which shows the structure of the power converter device which concerns on embodiment. FIG. 2A is an explanatory diagram of a first mode of the power conversion device according to the embodiment, and FIG. 2B is an explanatory diagram of a second mode of the power conversion device according to the embodiment. FIG. 3A is an explanatory diagram of a third mode of the power conversion device according to the embodiment, and FIG. 3B is an explanatory diagram of a fourth mode of the power conversion device according to the embodiment. 4A is an explanatory diagram of a fifth mode of the power conversion device according to the embodiment, and FIG. 4B is an explanatory diagram of a sixth mode of the power conversion device according to the embodiment. FIG. 5A is an explanatory diagram of a seventh mode of the power conversion device according to the embodiment, and FIG. 5B is an explanatory diagram of an eighth mode of the power conversion device according to the embodiment. It is a wave form diagram of the final output voltage of the power converter concerning an embodiment. It is the schematic which shows the structure of the power conditioner which concerns on embodiment. 8A is an explanatory diagram of a single-side discharge mode in which only the first capacitor of the power conversion device according to the embodiment is discharged, and FIG. 8B is an explanatory diagram of a single-side discharge mode in which only the second capacitor of the power conversion device according to the embodiment is discharged. 9A is an explanatory diagram of a single-side discharge mode in which only the first capacitor of the power conversion device according to the embodiment is discharged, and FIG. 9B is an explanatory diagram of a single-side discharge mode in which only the second capacitor of the power conversion device according to the embodiment is discharged. It is a flowchart which shows operation | movement of the power converter device which concerns on embodiment.

  As shown in FIG. 1, the power conversion apparatus 1 according to the present embodiment includes a first conversion circuit 11 and a second conversion circuit 12, and further includes a first bidirectional switch 13 and a second bidirectional switch 14. And a control unit 6.

  The first conversion circuit 11 and the second conversion circuit 12 are electrically connected between a first input point 101 on the high potential side of the DC power supply 100 and a second input point 102 on the low potential side of the DC power supply 100. Connected in parallel.

  The first conversion circuit 11 includes first to fourth switching elements Q1 to Q4 and a first capacitor C1. Here, the first conversion circuit 11 sets a connection point between the second switching element Q <b> 2 and the third switching element Q <b> 3 as the first output point 103.

  The first to fourth switching elements Q1 to Q4 are electrically connected in series between the first input point 101 and the second input point 102. The first to fourth switching elements Q1 to Q4 are in the order of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 from the first input point 101 side. Connected in series. The first capacitor C1 is electrically connected in parallel with the series circuit of the second switching element Q2 and the third switching element Q3.

  The second conversion circuit 12 includes fifth to eighth switching elements Q5 to Q8 and a second capacitor C2. Here, the second conversion circuit 12 sets a connection point between the sixth switching element Q6 and the seventh switching element Q7 as the second output point 104.

  The fifth to eighth switching elements Q5 to Q8 are electrically connected in series between the first input point 101 and the second input point 102. The fifth to eighth switching elements Q5 to Q8 are in the order of the fifth switching element Q5, the sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 from the first input point 101 side. Connected in series. The second capacitor C2 is electrically connected in parallel with the series circuit of the sixth switching element Q6 and the seventh switching element Q7.

  The first bidirectional switch 13 is a connection point between the first connection point 201, which is a connection point between the first switching element Q1 and the second switching element Q2, and a connection point between the seventh switching element Q7 and the eighth switching element Q8. It is electrically connected to a certain second connection point 202.

  The second bidirectional switch 14 is a connection point between the third connection element 203, which is a connection point between the third switching element Q3 and the fourth switching element Q4, and a connection point between the fifth switching element Q5 and the sixth switching element Q6. It is electrically connected to a certain fourth connection point 204.

  The control unit 6 controls the first to eighth switching elements Q1 to Q8 and the first and second bidirectional switches 13 and 14 to thereby control the DC power supply 100 and the first output point 103 for the first output point 103 and the second output point 104. The connection state between the first capacitor C1 and the second capacitor C2 is switched. Thereby, the control part 6 changes the magnitude | size of the output voltage produced between the 1st output point 103 and the 2nd output point 104 in several steps.

  Further, the control unit 6 includes the first to eighth switching elements so as to enter the one-side discharge mode when the difference between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 exceeds a predetermined threshold. Q1 to Q8 and the first and second bidirectional switches 13 and 14 are controlled. As will be described later in detail, the one-side discharge mode here is a mode in which only the capacitor having the higher voltage of the first capacitor C1 and the second capacitor C2 is discharged.

  According to this configuration, when the difference between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 exceeds a predetermined threshold, the power conversion device 1 has the first capacitor C1 and the second capacitor C2. In this mode, only the capacitor having the higher voltage is discharged. In other words, the power conversion device 1 discharges only the capacitor with the higher voltage even when the voltage imbalance (imbalance) of the pair of capacitors (the first capacitor C1 and the second capacitor C2) occurs. It is possible to balance the voltage of the capacitors. Therefore, the power conversion device 1 has an advantage that the withstand voltage required for the capacitor can be lowered by balancing the voltages of the pair of capacitors.

  Moreover, the power conversion device 1 balances the voltages of the pair of capacitors by discharging one of the capacitors when the voltage imbalance of the pair of capacitors occurs. That is, since the power conversion device 1 is configured to discharge instead of charging only one capacitor, when the voltage imbalance occurs, the first capacitor C1 and the second capacitor C2 are supplied from the DC power supply 100. Operates in an electrically disconnected state. Therefore, the power conversion device 1 can prevent the occurrence of leakage current due to the voltage imbalance of the pair of capacitors.

  Hereinafter, the power converter 1 according to the present embodiment and the power conditioner 20 (see FIG. 7) using the power converter 1 will be described in detail. However, the configuration described below is only an example of the present invention, and the present invention is not limited to the following embodiment, and the technical idea according to the present invention is not deviated from this embodiment. Various changes can be made in accordance with the design or the like as long as they are not.

  In the present embodiment, the case where the power conditioner 20 is a residential power conditioner that is used by being electrically connected to a photovoltaic power generation device serving as the DC power source 100 is exemplified. However, the use of the power conditioner 20 is illustrated. It is not intended to limit. The power conditioner 20 may be used by being electrically connected to a DC power source 100 other than a solar power generation device, such as a household fuel cell or a power storage device, or a non-residential such as a store, factory, office, etc. May be used. Furthermore, the power converter 1 is not intended to limit the application to the power conditioner 20, and the power converter 1 may be used other than the power conditioner 20.

<Configuration of power converter>
The power converter 1 of this embodiment is electrically connected to the DC power supply 100 as shown in FIG. Here, since the DC power source 100 is composed of a solar power generation device, the power conversion device 1 is connected to the DC power source 100 via a connection box.

  The power conversion device 1 of the present embodiment further includes a filter circuit 5, a first detection unit 21, and a second detection unit 22 in addition to the conversion circuit 10 and the control unit 6. The conversion circuit 10 includes a first conversion circuit 11 and a second conversion circuit 12, and a first bidirectional switch 13 and a second bidirectional switch 14.

  The first input point 101 and the second input point 102 serve as a pair of input terminals in the power converter 1, and the DC power source 100 is electrically connected between the pair of input terminals (the first input point 101 and the second input point 102). Connected.

  The first output point 103 of the first conversion circuit 11 and the second output point 104 of the second conversion circuit 12 are electrically connected to the third output point 105 and the fourth output point 106 through the filter circuit 5, respectively. Has been. In the present embodiment, the third output point 105 and the fourth output point 106 serve as a pair of output terminals in the power conversion device 1.

  In the present embodiment, the output voltage of the power conversion device 1 is an AC voltage, and the third output point 105 and the fourth output point 106 are electrically connected to the system power supply (commercial power system) 7. Further, the third output point 105 and the fourth output point 106 are electrically connected to a load 8 that operates by receiving supply of AC power.

  Specifically, the pair of output terminals of the power conversion device 1 is connected to the load 8 and the system power supply 7 by being electrically connected to an interconnection breaker provided in the distribution board. That is, the power conversion device 1 converts the DC power input from the DC power source 100 into AC power, and the AC power is transferred from the pair of output terminals (the third output point 105 and the fourth output point 106) to the load 8 and the system. Output to power supply 7. In FIG. 1, the system power supply 7 is a single-phase three-wire system having a U-phase and a W-phase. However, the system power supply 7 may be a single-phase two-wire system without being limited to this example.

  Next, the structure of each part of the power converter device 1 will be described in detail.

  The power conversion apparatus 1 uses the input terminal on the high potential (positive electrode) side of the DC power supply 100 among the pair of input terminals connected to the DC power supply 100 as the first input point 101, and the low potential (negative electrode) of the DC power supply 100. The input terminal on the side is the second input point 102. Therefore, a DC voltage output from the DC power supply 100 is applied as an input voltage between the first input point 101 and the second input point 102.

  Here, it is assumed that the input terminal (second input point 102) on the low potential side of the DC power supply 100 is the circuit ground of the power converter 1, and the potential thereof is 0 [V]. Then, the potential of the first input point 101 is expressed by E [V] using the DC voltage E [V] output from the DC power supply 100.

  As described above, the first conversion circuit 11 includes the first to fourth switching elements Q1 to Q4 connected in series between the first input point 101 and the second input point 102, and the first capacitor C1. doing. For each of the first to fourth switching elements Q1 to Q4, a depletion type n-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) is used here as an example.

  The drain of the first switching element Q1 is electrically connected to the first input point 101. The drain of the second switching element Q2 is electrically connected to the source of the first switching element Q1. The drain of the third switching element Q3 is electrically connected to the source of the second switching element Q2. The drain of the fourth switching element Q4 is electrically connected to the source of the third switching element Q3. Further, the source of the fourth switching element Q 4 is electrically connected to the second input point 102.

  Here, the source of the second switching element Q 2 (the drain of the third switching element Q 3) is the first output point 103. Furthermore, the source of the first switching element Q1 (the drain of the second switching element Q2) is the first connection point 201, and the source of the third switching element Q3 (the drain of the fourth switching element Q4) is the third connection. A point 203 is obtained.

  One end of the first capacitor C1 is electrically connected to the drain (first connection point 201) of the second switching element Q2, and the other end is electrically connected to the source (third connection point 203) of the third switching element Q3. Connected. In other words, the first capacitor C1 has one end electrically connected to the first input point 101 via the first switching element Q1 and the other end connected to the second input point 102 via the fourth switching element Q4. Electrically connected.

  As described above, the second conversion circuit 12 includes the fifth to eighth switching elements Q5 to Q8 connected in series between the first input point 101 and the second input point 102, and the second capacitor C2. doing. Here, the second conversion circuit 12 has basically the same configuration as the first conversion circuit 11, and the fifth to eighth switching elements Q5 to Q8 correspond to the first to fourth switching elements Q1 to Q4. The second capacitor C2 corresponds to the first capacitor C1. Here, depletion type n-channel MOSFETs are used for the fifth to eighth switching elements Q5 to Q8, similarly to the first to fourth switching elements Q1 to Q4.

  That is, the drain of the fifth switching element Q5 is electrically connected to the first input point 101. The drain of the sixth switching element Q6 is electrically connected to the source of the fifth switching element Q5. The drain of the seventh switching element Q7 is electrically connected to the source of the sixth switching element Q6. The drain of the eighth switching element Q8 is electrically connected to the source of the seventh switching element Q7. Further, the source of the eighth switching element Q8 is electrically connected to the second input point 102.

  Here, the source of the sixth switching element Q 6 (the drain of the seventh switching element Q 7) is the second output point 104. Further, the source of the fifth switching element Q5 (the drain of the sixth switching element Q6) is the fourth connection point 204, and the source of the seventh switching element Q7 (the drain of the eighth switching element Q8) is the second connection point. A point 202 is obtained.

  The second capacitor C2 has one end electrically connected to the drain (fourth connection point 204) of the sixth switching element Q6 and the other end electrically connected to the source (second connection point 202) of the seventh switching element Q7. Connected. In other words, the second capacitor C2 has one end electrically connected to the first input point 101 via the fifth switching element Q5 and the other end connected to the second input point 102 via the eighth switching element Q8. Electrically connected.

  The circuit constant (capacitance) of the second capacitor C2 is equal to the circuit constant (capacitance) of the first capacitor C1.

  In FIG. 1, first to eighth diodes D1 to D8 are connected in antiparallel to the first to eighth switching elements Q1 to Q8, respectively. The first to eighth diodes D1 to D8 are parasitic diodes of the first to eighth switching elements Q1 to Q8, respectively. That is, the parasitic diode of the first switching element Q1 constitutes the first diode D1, and similarly, the parasitic diodes of the second, third,... Switching elements Q2, Q3,. , D3. For example, the first diode D1 is connected in a direction in which the drain side of the first switching element Q1 is a cathode and the source side is an anode.

  The first conversion circuit 11 and the second conversion circuit 12 configured as described above are electrically connected in parallel between the first input point 101 and the second input point 102. That is, the first conversion circuit 11 and the second conversion circuit 12 are connected in parallel between both ends of the DC power supply 100.

  The first bidirectional switch 13 is electrically connected between the first connection point 201 and the second connection point 202. That is, the first connection point 201 of the first conversion circuit 11 is electrically connected to the second connection point 202 of the second conversion circuit 12 via the first bidirectional switch 13. Here, the first bidirectional switch 13 includes a ninth switching element Q9 and a tenth switching element Q10 electrically connected in series between the first connection point 201 and the second connection point 202. have. The first bidirectional switch 13 is connected in the order of the ninth switching element Q9 and the tenth switching element Q10 from the first connection point 201 side.

  More specifically, a depletion type n-channel MOSFET is used for each of the ninth and tenth switching elements Q9 and Q10, similarly to each of the first to eighth switching elements Q1 to Q8. The source of the ninth switching element Q9 is connected to the first connection point 201, and the drain of the ninth switching element Q9 is connected to the drain of the tenth switching element Q10. The source of the tenth switching element Q <b> 10 is connected to the second connection point 202. In short, the ninth switching element Q9 and the tenth switching element Q10 are connected in anti-series between the first connection point 201 and the second connection point 202 so that the drains are connected to each other. .

  The second bidirectional switch 14 is electrically connected between the third connection point 203 and the fourth connection point 204. That is, the third connection point 203 of the first conversion circuit 11 is electrically connected to the fourth connection point 204 of the second conversion circuit 12 via the second bidirectional switch 14. Here, the second bidirectional switch 14 includes the twelfth switching element Q12 and the eleventh switching element Q11 electrically connected in series between the third connection point 203 and the fourth connection point 204. have. The second bidirectional switch 14 is connected in the order of the twelfth switching element Q12 and the eleventh switching element Q11 from the third connection point 203 side.

  More specifically, a depletion type n-channel MOSFET is used for each of the eleventh and twelfth switching elements Q11 and Q12, similarly to each of the first to eighth switching elements Q1 to Q8. The source of the eleventh switching element Q11 is connected to the fourth connection point 204, and the drain of the eleventh switching element Q11 is connected to the drain of the twelfth switching element Q12. The source of the twelfth switching element Q12 is connected to the third connection point 203. In short, the eleventh switching element Q11 and the twelfth switching element Q12 are connected in anti-series between the third connection point 203 and the fourth connection point 204 so that the drains are connected to each other. .

  Also, ninth to twelfth diodes D9 to D12 are connected in antiparallel to the ninth to twelfth switching elements Q9 to Q12, respectively. The ninth to twelfth diodes D9 to D12 are parasitic diodes of the ninth to twelfth switching elements Q9 to Q12, respectively. That is, the parasitic diode of the ninth switching element Q9 constitutes the ninth diode D9, and similarly, the parasitic diodes of the tenth, eleventh and twelfth switching elements Q10, Q11 and Q12 are the tenth, eleventh and twelfth elements, respectively. Diodes D10, D11, D12. For example, the ninth diode D9 is connected in such a direction that the drain side of the ninth switching element Q9 is a cathode and the source side is an anode.

  In the present embodiment, the first bidirectional switch 13 is configured to be able to switch between operation states including an all-off state and an all-on state. The all-off state of the first bidirectional switch 13 is a state in which a bidirectional current is interrupted between the first connection point 201 and the second connection point 202. The all-on state of the first bidirectional switch 13 is a state in which bidirectional current passes between the first connection point 201 and the second connection point 202. Similarly, the second bidirectional switch 14 is configured to be able to switch the operation state including the all-off state and the all-on state. The all-off state of the second bidirectional switch 14 is a state in which bidirectional current is interrupted between the third connection point 203 and the fourth connection point 204. The all-on state of the second bidirectional switch 14 is a state in which bidirectional current passes between the third connection point 203 and the fourth connection point 204.

  Furthermore, in the present embodiment, the operation state of the first bidirectional switch 13 is such that the current flowing from the second connection point 202 to the first connection point 201 is cut off, and the first connection point 201 to the second connection point 202. It further includes a half-on state for passing a flowing current. Further, the operating state of the second bidirectional switch 14 blocks the current flowing from the third connection point 203 to the fourth connection point 204 and allows the current flowing from the fourth connection point 204 to the third connection point 203 to pass. It further includes a semi-on state.

  Therefore, in the power conversion device 1 of the present embodiment, bidirectional current can pass between the first connection point 201 and the second connection point 202 by setting the first bidirectional switch 13 to the all-on state. Can create a unique state. Moreover, the power converter device 1 of this embodiment can pass a bidirectional | two-way electric current between the 3rd connection point 203 and the 4th connection point 204 by making the 2nd bidirectional switch 14 all the ON states. Can create a unique state.

  That is, the first bidirectional switch 13 is turned off when the ninth and tenth switching elements Q9 and Q10 are both off, and the ninth and tenth switching elements Q9 and Q10 are both on. All are turned on. Further, in the first bidirectional switch 13, when the tenth switching element Q10 is on and the ninth switching element Q9 is off, the direction of current is restricted to one direction by the ninth diode D9. Semi-on state.

  Further, the second bidirectional switch 14 is fully turned off when the eleventh and twelfth switching elements Q11 and Q12 are both off, and the eleventh and twelfth switching elements Q11 and Q12 are both on. All are turned on. Further, in the second bidirectional switch 14, when the twelfth switching element Q12 is on and the eleventh switching element Q11 is off, the direction of the current is limited to one direction by the eleventh diode D11. Semi-on state.

  As described above, the bidirectional switch (each of the first bidirectional switch 13 and the second bidirectional switch 14) in the present embodiment has three operation states consisting of a full-off state, a full-on state, and a half-on state. Can be switched.

  In other words, the first bidirectional switch 13 is electrically connected between the positive terminal of the first capacitor C1 and the negative terminal of the second capacitor C2. The second bidirectional switch 14 is electrically connected between the negative terminal of the first capacitor C1 and the positive terminal of the second capacitor C2. That is, the first capacitor C1 of the first conversion circuit 11 and the second capacitor C2 of the second conversion circuit 12 are connected in a crossed manner via the first bidirectional switch 13 and the second bidirectional switch 14. Has been.

  Furthermore, the gates of the first to eighth switching elements Q1 to Q8 and the ninth to twelfth switching elements Q9 to Q12 are electrically connected to the control unit 6, respectively. The control unit 6 can individually switch on / off the first to fourth switching elements Q <b> 1 to Q <b> 4 and thereby controls the first conversion circuit 11. The control unit 6 can individually switch on / off the fifth to eighth switching elements Q5 to Q8, and thereby controls the second conversion circuit 12. The controller 6 can individually switch on / off the ninth and tenth switching elements Q9 and Q10, and thereby controls the first bidirectional switch 13. The controller 6 can individually switch on / off the eleventh and twelfth switching elements Q11 and Q12, and thereby controls the second bidirectional switch 14.

  Note that the control unit 6 may be provided individually for each of the first conversion circuit 11, the second conversion circuit 12, the first bidirectional switch 13, and the second bidirectional switch 14.

  In the present embodiment, the control unit 6 includes a drive circuit 61 that supplies a drive signal to the first to twelfth switching elements Q1 to Q12, and a microcomputer (microcomputer) 62 that supplies a signal to the drive circuit 61.

  The drive circuit 61 is configured to drive (control) each element individually by giving a drive signal to the control terminals (gates) of the first to twelfth switching elements Q1 to Q12. The microcomputer 62 is configured to control the drive circuit 61 by giving a PWM (Pulse Width Modulation) signal to the drive circuit 61. That is, the control unit 6 individually controls the first to twelfth switching elements Q1 to Q12 by a drive signal generated by the drive circuit 61 in response to an instruction from the microcomputer 62.

  Here, it is preferable that the drive circuit 61 also has a function as a short-circuit prevention circuit that prevents two or more switching elements from being simultaneously turned on to prevent a short-circuit current from flowing. That is, when switching elements of a specific combination are simultaneously turned on, for example, the first input point 101 and the second input point 102 are short-circuited, and the current from the DC power supply 100 may flow as a short-circuit current to the switching element. There is. Therefore, it is preferable that the drive circuit 61 is configured such that such specific combination of switching elements does not turn on at the same time. For example, when the drive signals input to the gates of a specific combination of switching elements simultaneously become H level, the drive circuit 61 forcibly lowers the drive signal to L level to simultaneously turn on the specific combination of switching elements. It is configured not to let you.

  As shown in FIG. 1, the filter circuit 5 has a pair of inductors L1 and L2 and a third capacitor C3. One inductor L <b> 1 is electrically connected between the first output point 103 and the third output point 105. The other inductor L 2 is electrically connected between the second output point 104 and the fourth output point 106. However, if the inductors L1 and L2 are electrically connected between at least one of the first output point 103 and the second output point 104 and the output terminal (the third output point 105 and the fourth output point 106). Any one of the inductors L1 and L2 may be omitted.

  The third capacitor C <b> 3 is electrically connected between the third output point 105 and the fourth output point 106. In other words, the filter circuit 5 is a series circuit of an inductor L1, a third capacitor C3, and an inductor L2 that are electrically connected between the first output point 103 and the second output point 104.

  The first detection unit 21 is configured to detect the voltage of the first capacitor C1. Here, the 1st detection part 21 detects the magnitude | size of the voltage V1 which generate | occur | produces at the both ends of the 1st capacitor C1, using the 1st connection point 201 side as a positive electrode. The first detection unit 21 includes a pair of voltage dividing resistors connected in series between the first connection point 201 and the third connection point 203, for example. However, the structure of the 1st detection part 21 is not restricted to this, What is necessary is just a structure which can detect the value (magnitude | size) of the voltage (both-ends voltage) V1 which generate | occur | produces at the both ends of the 1st capacitor C1. The first detection unit 21 outputs the value of the voltage V <b> 1 as a detection result to the microcomputer 62 of the control unit 6.

  The second detection unit 22 is configured to detect the voltage of the second capacitor C2. Here, the 2nd detection part 22 detects the magnitude | size of the voltage V2 which generate | occur | produces at the both ends of the 2nd capacitor C2 by making the 4th connection point 204 side into a positive electrode. The second detection unit 22 includes, for example, a pair of voltage dividing resistors connected in series between the fourth connection point 204 and the second connection point 202. However, the configuration of the second detection unit 22 is not limited to this, and may be any configuration that can detect the value (magnitude) of the voltage (voltage across both ends) V2 generated at both ends of the second capacitor C2. The second detection unit 22 outputs the value of the voltage V <b> 2 that is the detection result to the microcomputer 62 of the control unit 6.

  The operation of the control unit 6 using the detection results of the first detection unit 21 and the second detection unit 22 will be described later.

<Basic operation of power converter>
The basic operation of the power conversion device 1 configured as described above will be briefly described with reference to FIGS. 2A, 2B, 3A, 3B, 4A, 4B, 5A, and 5B. In the drawing, a thick arrow represents a current path, and a switching element with a dotted circle represents an on-state element.

  The basic operation of the power conversion device 1 here is a period from when the supply of power from the DC power supply 100 is started until the first capacitor C1 and the second capacitor C2 are charged to the reference voltage (hereinafter referred to as “starting period”). The operation of the power conversion apparatus 1 after elapse of “)”. That is, the operation of the power conversion device 1 from the state where the first capacitor C1 and the second capacitor C2 are charged to the reference voltage is defined as the basic operation of the power conversion device 1.

  The reference voltage for the first capacitor C <b> 1 is a voltage that is ¼ of the applied voltage applied from the DC power source 100 between the first input point 101 and the second input point 102. Similarly, the reference voltage for the second capacitor C <b> 2 is a voltage that is ¼ of the applied voltage applied between the first input point 101 and the second input point 102 from the DC power supply 100.

  In the following, it is assumed that the output voltage of the DC power supply 100 is E [V], the potential of the first input point 101 is E [V], and the potential of the second input point 102 is 0 [V]. Here, the voltage across each of the first capacitor C1 and the second capacitor C2 charged to the reference voltage is E / 4 [V]. Hereinafter, a potential difference between the first output point 103 and the second output point 104, that is, a voltage generated between the first output point 103 and the second output point 104 will be described as an output voltage of the power conversion device 1.

  Since the third output point 105 and the fourth output point 106 are electrically connected to the system power supply 7, the potential difference between the third output point 105 and the fourth output point 106, that is, the third output point 105-the second output point. The voltage generated between the four output points 106 is equal to the output voltage of the system power supply 7. The potential difference between the first output point 103 and the third output point 105 and the potential difference between the second output point 104 and the fourth output point 106 are absorbed by the filter circuit 5.

  The power conversion device 1 switches the first conversion circuit 11, the second conversion circuit 12, the first bidirectional switch 13, and the second bidirectional switch 14 to a total of eight modes 1 to 8. As a result, the power conversion device 1 converts the DC voltage (E [V]) applied between the first input point 101 and the second input point 102 into an AC voltage, and the first output point 103 and the first input point 103 An output voltage is generated between the two output points 104. In the following description, the first to twelfth switching elements Q1 to Q12 are assumed to be in the “off” state when the on / off state is not mentioned. Further, it is assumed that the voltage drop in the first to twelfth switching elements Q1 to Q12 and the voltage drop in the first to twelfth diodes D1 to D12 are negligible.

  Here, the control part 6 controls the 1st-12th switching elements Q1-Q12 according to the following two conditions. However, these conditions are conditions applied to the first to eighth modes, and are not applied to the one-side discharge mode described later.

  As a first condition, a one-to-one pair is set by the first to fourth switching elements Q1 to Q4 of the first conversion circuit 11 and the fifth to eighth switching elements Q5 to Q8 of the second conversion circuit 12. On / off is switched for each pair. Here, the first and eighth switching elements Q1, Q8 are paired, the second, seventh switching elements Q2, Q7 are paired, the third, sixth switching elements Q3, Q6 are paired, and the fourth, fifth Switching elements Q4 and Q5 form a pair.

  The second condition is that the second switching element Q2 and the third switching element Q3 are not simultaneously turned on or off. Further, in the first to fourth modes, the first switching element Q1 and the eleventh switching element Q11, and in the fifth to eighth modes, the fourth switching element Q4 and the ninth switching element Q9, Are not simultaneously turned on or off.

  First, in the first mode shown in FIG. 2A, the first and second switching elements Q1 and Q2 of the first conversion circuit 11, the seventh and eighth switching elements Q7 and Q8 of the second conversion circuit 12, and the second Each of the twelfth switching elements Q12 of the bidirectional switch 14 is in an ON state. That is, the second bidirectional switch 14 is in a half-on state. In this state, as shown in FIG. 2A, the first input point 101 is electrically connected to the first output point 103 via the first switching element Q1 and the second switching element Q2. The second input point 102 is electrically connected to the second output point 104 via the eighth switching element Q8 and the seventh switching element Q7. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, i.e., first, second, seventh, and eighth switching elements Q1, Q2, Q7, and Q8. There is no current flowing through.

  Accordingly, the first output point 103 has the same potential (E [V]) as the first input point 101, and the second output point 104 has the same potential (0 [V]) as the second input point 102. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 is E (= E-0) [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2.

  Next, in the second mode shown in FIG. 2B, the first and third switching elements Q1 and Q3 of the first conversion circuit 11, the sixth and eighth switching elements Q6 and Q8 of the second conversion circuit 12, Each of the two bidirectional switches 14 and the twelfth switching element Q12 is in an ON state. That is, the second bidirectional switch 14 is in a half-on state. In this state, as shown in FIG. 2B, the first input point 101 is electrically connected to the first output point 103 via the first switching element Q1, the first capacitor C1, and the third switching element Q3. The The second input point 102 is electrically connected to the second output point 104 via the eighth switching element Q8, the second capacitor C2, and the sixth switching element Q6. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, that is, the first, third, sixth, and eighth switching elements Q1, Q3, Q6, and Q8, and the twelfth switching element Q12. There is no current flowing through.

  Therefore, the potential of the first output point 103 is lower than the potential (E [V]) of the first input point 101 by the voltage across the first capacitor C1 (E / 4 [V]), that is, 3E / 4 ( = EE-4) [V]. The potential of the second output point 104 is higher than the potential of the second input point 102 (0 [V]) by the voltage across the second capacitor C2 (E / 4 [V]), that is, E / 4 ( = 0 + E / 4) [V]. Therefore, the output voltage of the power converter 1 generated between the first output point 103 and the second output point 104 is E / 2 (= 3E / 4-E / 4) [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2.

  Next, in the third mode shown in FIG. 3A, the second switching element Q2 of the first conversion circuit 11, the seventh switching element Q7 of the second conversion circuit 12, and the second bidirectional switch 14 11 and 12 switching elements Q11 and Q12 are in an ON state, respectively. That is, the second bidirectional switch 14 is in an all-on state. In this state, the second output point 104 passes through the seventh switching element Q7, the second capacitor C2, the eleventh switching element Q11, the twelfth switching element Q12, the first capacitor C1, and the second switching element Q2. And electrically connected to the first output point 103. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, the second, seventh, eleventh, and twelfth switching elements Q2, Q7, Q11, and Q12.

  Accordingly, the potential at the first output point 103 is determined by the voltage across the first capacitor C1 (E / 4 [V]) and the voltage across the second capacitor C2 (E / 4 [V]) from the potential at the second output point 104. ) And a higher potential. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 becomes E / 2 (= E / 4 + E / 4) [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2. In this state, since the second bidirectional switch 14 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  Next, in the fourth mode shown in FIG. 3B, the third switching element Q3 of the first conversion circuit 11, the sixth switching element Q6 of the second conversion circuit 12, and the second bidirectional switch 14 are switched. 11 and 12 switching elements Q11 and Q12 are in an ON state, respectively. That is, the second bidirectional switch 14 is in an all-on state. In this state, the second output point 104 is electrically connected to the first output point 103 via the sixth switching element Q6, the eleventh switching element Q11, the twelfth switching element Q12, and the third switching element Q3. Connected. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, third, sixth, eleventh, and twelfth switching elements Q3, Q6, Q11, and Q12.

  Therefore, the potential at the first output point 103 is the same as that at the second output point 104. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 is 0 [V]. Further, at this time, the potential of the third output point 105 becomes a potential obtained by subtracting the voltage across the inductor L1 from the potential of the first output point 103, and the potential of the fourth output point 106 becomes the potential of the second output point 104 to the inductor. The potential is the sum of the voltages at both ends of L2. In this state, since the second bidirectional switch 14 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  On the other hand, in the fifth to eighth modes, the power conversion device 1 switches the operation between the first conversion circuit 11 and the second conversion circuit 12 based on the first to fourth modes. The bi-directional switch 13 and the second bi-directional switch 14 perform operations that are interchanged. That is, in the fifth to eighth modes and the first to fourth modes, the operation of the conversion circuit 10 is the first conversion circuit 11 and the first bidirectional switch 13, and the second conversion circuit 12 and the second mode. The direction switch 14 is replaced with a symmetrical operation.

  That is, in the fifth mode shown in FIG. 4A, the operation of the conversion circuit 10 is symmetric to the fourth mode. Therefore, in the fifth mode, the second switching element Q2 of the first conversion circuit 11, the seventh switching element Q7 of the second conversion circuit 12, and the ninth and tenth switching of the first bidirectional switch 13 are switched. Elements Q9 and Q10 are each in an on state. That is, the first bidirectional switch 13 is fully turned on. In this state, as shown in FIG. 4A, the first output point 103 is connected to the second switching element Q2, the ninth switching element Q9, the tenth switching element Q10, and the seventh switching element Q7 through the second switching element Q2. It is electrically connected to the output point 104. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, the second, seventh, ninth, and tenth switching elements Q2, Q7, Q9, and Q10.

  Therefore, the potential at the first output point 103 is the same as that at the second output point 104. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 is 0 [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2. In this state, since the first bidirectional switch 13 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  Next, in the sixth mode shown in FIG. 4B, the operation of the conversion circuit 10 is symmetric to the third mode. Therefore, in the sixth mode, the third switching element Q3 of the first conversion circuit 11, the sixth switching element Q6 of the second conversion circuit 12, and the ninth and tenth switching of the first bidirectional switch 13 are switched. Elements Q9 and Q10 are each in an on state. That is, the first bidirectional switch 13 is fully turned on. In this state, the first output point 103 passes through the third switching element Q3, the first capacitor C1, the ninth switching element Q9, the tenth switching element Q10, the second capacitor C2, and the sixth switching element Q6. And electrically connected to the second output point 104. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, that is, third, sixth, ninth, and tenth switching elements Q3, Q6, Q9, and Q10.

  Accordingly, the potential at the first output point 103 is determined by the voltage across the first capacitor C1 (E / 4 [V]) and the voltage across the second capacitor C2 (E / 4 [V]) from the potential at the second output point 104. ) And a lower potential. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 becomes −E / 2 (= −E / 4−E / 4) [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2. In this state, since the first bidirectional switch 13 is fully on, the conversion circuit 10 can cause a bidirectional current to flow between the first output point 103 and the second output point 104. it can.

  Next, in the seventh mode shown in FIG. 5A, the operation of the conversion circuit 10 is symmetric to the second mode. Therefore, in the seventh mode, the second and fourth switching elements Q2 and Q4 of the first conversion circuit 11, the fifth and seventh switching elements Q5 and Q7 of the second conversion circuit 12, and the first bidirectional switch The thirteenth switching elements Q10 are in the on state. That is, the first bidirectional switch 13 is in a half-on state. In this state, as shown in FIG. 5A, the first input point 101 is electrically connected to the second output point 104 via the fifth switching element Q5, the second capacitor C2, and the seventh switching element Q7. The The second input point 102 is electrically connected to the first output point 103 via the fourth switching element Q4, the first capacitor C1, and the second switching element Q2. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, ie, the second, fourth, fifth, and seventh switching elements Q2, Q4, Q5, and Q7, and the tenth switching element Q10. There is no current flowing through.

  Therefore, the potential of the first output point 103 is higher than the potential of the second input point 102 (0 [V]) by the voltage across the first capacitor C1 (E / 4 [V]), that is, E / 4 ( = 0 + E / 4) [V]. The potential of the second output point 104 is lower than the potential of the first input point 101 (E [V]) by the voltage across the second capacitor C2 (E / 4 [V]), that is, 3E / 4 ( = EE-4) [V]. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 becomes −E / 2 (= E / 4-3E / 4) [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2.

  Next, in the eighth mode shown in FIG. 5B, the operation of the conversion circuit 10 is symmetric with respect to the first mode. Therefore, in the eighth mode, the third and fourth switching elements Q3 and Q4 of the first conversion circuit 11, the fifth and sixth switching elements Q5 and Q6 of the second conversion circuit 12, and the first bidirectional switch. The thirteenth switching elements Q10 are in the on state. That is, the first bidirectional switch 13 is in a half-on state. In this state, as shown in FIG. 5B, the first input point 101 is electrically connected to the second output point 104 via the fifth switching element Q5 and the sixth switching element Q6. The second input point 102 is electrically connected to the first output point 103 via the fourth switching element Q4 and the third switching element Q3. At this time, among the semiconductor elements (switching elements, diodes), there are a total of four elements, that is, the third, fourth, fifth, and sixth switching elements Q3, Q4, Q5, and Q6, and the tenth switching element Q10. There is no current flowing through.

  Therefore, the first output point 103 has the same potential (0 [V]) as the second input point 102, and the second output point 104 has the same potential (E [V]) as the first input point 101. Therefore, the output voltage of the power conversion device 1 generated between the first output point 103 and the second output point 104 is −E (= 0−E) [V]. Further, at this time, the potential at the third output point 105 is a potential obtained by adding the voltage across the inductor L1 to the potential at the first output point 103, and the potential at the fourth output point 106 is changed from the potential at the second output point 104 to the inductor. The potential is obtained by subtracting the voltage across L2.

  In short, the power conversion device 1 changes the magnitude of the output voltage generated between the first output point 103 and the second output point 104 in a plurality of stages by switching the first to eighth modes.

  More specifically, the first conversion circuit 11 uses the first capacitor C1 as a flying capacitor, and switches the first to fourth, ninth to twelfth switching elements Q1 to Q4 and Q9 to Q12 on / off, thereby The potential at one output point 103 is switched. In principle, the first capacitor C1 is charged in the second and seventh modes and discharged in the third and sixth modes. However, if the first to eighth modes are switched at a relatively high frequency, the first capacitor C1 is operated during basic operation. The voltage across the first capacitor C1 can be regarded as substantially constant (E / 4 [V]).

  The second conversion circuit 12 uses the second capacitor C2 as a flying capacitor, and switches the potential of the second output point 104 by switching on / off the fifth to twelfth switching elements Q5 to Q12. In principle, the second capacitor C2 is charged in the second and seventh modes and discharged in the third and sixth modes. However, if the first to eighth modes are switched at a relatively high frequency, the second capacitor C2 is operated during basic operation. The voltage across the second capacitor C2 can be regarded as substantially constant (E / 4 [V]).

  In short, the control unit 6 charges the capacitor by switching between a pair of modes in which the magnitude of the output voltage is the same and the directions of the currents flowing through the capacitors (the first capacitor C1 and the second capacitor C2) are reversed. And switching between discharge.

  Specifically, when the output voltage is set to E / 2 [V], the control unit 6 switches the second mode and the third mode as a pair of modes, thereby changing the capacitor (first capacitor C1). And switching between charging and discharging of the second capacitor C2). In addition, when the output voltage is set to −E / 2 [V], the control unit 6 switches the seventh mode and the sixth mode as a pair of modes so that the capacitors (the first capacitor C1 and the first mode) are switched. Switching between charging and discharging of the two capacitors C2).

  Here, since the first capacitor C1 and the second capacitor C2 are charged in the second and seventh modes in principle, the second mode and the seventh mode are also referred to as “charging modes” below. Since the first capacitor C1 and the second capacitor C2 are discharged in the third and sixth modes in principle, the third mode and the sixth mode are also referred to as “discharge modes” below. In the following description, the control unit 6 outputs a “charge command” when selecting the charge mode, and outputs a “discharge command” when selecting the discharge mode.

  That is, when the output voltage is set to E / 2 [V], the control unit 6 outputs a charge command when charging the capacitors (the first capacitor C1 and the second capacitor C2), and is in the second charging mode. Select the mode. When the output voltage is set to E / 2 [V], the controller 6 outputs a discharge command when discharging the capacitors (the first capacitor C1 and the second capacitor C2), and the third mode which is the discharge mode. Select.

  Similarly, when the output voltage is set to −E / 2 [V], the control unit 6 outputs a charge command when charging the capacitors (the first capacitor C1 and the second capacitor C2), and is in the charging mode. Select the seventh mode. When the output voltage is set to −E / 2 [V], the control unit 6 outputs a discharge command when discharging the capacitors (the first capacitor C1 and the second capacitor C2), and is in the discharge mode. Select a mode.

  Thus, the control unit 6 switches the charging mode and the discharging mode in which the magnitude of the output voltage is the same and the direction of the current flowing through the capacitor is reversed as a pair of modes, thereby charging the capacitor. Switch between discharging and switching. However, the capacitor is charged in the charge mode and the capacitor is discharged in the discharge mode only when a forward current described later flows in the conversion circuit 10. In a state where a reverse current, which will be described later, flows in conversion circuit 10, the capacitor is discharged in the charge mode, and the capacitor is charged in the discharge mode. This point will be described later. Hereinafter, the description will be made assuming that the current flowing through the conversion circuit 10 is a forward current unless otherwise specified.

  As described above, in the first to eighth modes, the power conversion device 1 outputs, as an output voltage, a voltage having the first output point 103 as the high potential side and the second output point 104 as the low potential side. It will be. In the first to fourth modes, the power conversion apparatus 1 converts the output voltage generated between the first output point 103 and the second output point 104 to E [V] (first mode), E / 2. Switching is performed in three stages, [V] (second and third modes) and 0 [V] (fourth mode). In the fifth to eighth modes, the power conversion device 1 sets the output voltage generated between the first output point 103 and the second output point 104 to 0 [V] (fifth mode), −E / 2. [V] (6th and 7th mode) and -E [V] (8th mode) are switched in three stages.

  Therefore, the power conversion device 1 switches the output modes from E to 1 [V], E / 2 [V], 0 [V], and −E / 2 [V] by switching the first to eighth modes. , -E [V]. The power conversion apparatus 1 generates an AC voltage (hereinafter referred to as “final output voltage”) between the third output point 105 and the fourth output point 106 by appropriately switching these five-stage output voltages.

  Here, the final output voltage is equal to the output voltage of the system power supply 7, and has a sinusoidal waveform as shown in FIG. In FIG. 6, the horizontal axis represents the time axis and the vertical axis represents the voltage value. Here, in the period T1 to T3 in which the final output voltage varies in the range of 0 [V] to E [V] (that is, the period corresponding to the positive half-wave in the sine wave), the power converter 1 It operates by switching the first to fourth modes. In the period in which the final output voltage fluctuates in the range of 0 [V] to -E [V] (that is, the period corresponding to the negative half-wave in the sine wave) T4 to T6, the power conversion device 1 It operates by switching the mode of ~ 8.

  Table 1 summarizes the first to eighth modes described above.

  Here, the control part 6 switches on / off of the 1st-12th switching elements Q1-Q12 with a PWM signal, and implement | achieves the said 1st-8 mode.

  More specifically, in the periods T1 and T3 in which the final output voltage varies in the range of 0 [V] to E / 2 [V] in FIG. Repeat the operation to switch the mode. Here, the controller 6 balances the discharge and charge of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the second mode and the third mode.

  Further, in the period T2 in which the final output voltage fluctuates in the range of E / 2 [V] to E [V] in FIG. 6, the control unit 6 operates to switch the first to third modes as shown in Table 1. repeat. Here, the controller 6 balances the discharge and charge of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the second mode and the third mode.

  Further, in the periods T4 and T6 in which the final output voltage varies in the range of 0 [V] to -E / 2 [V] in FIG. 6, the control unit 6 performs the fifth to seventh modes as shown in Table 1. Repeat the operation of switching. Here, the control unit 6 balances the discharge and charge of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the sixth mode and the seventh mode.

  Further, in the period T5 in which the final output voltage varies in the range of −E / 2 [V] to −E [V] in FIG. 6, the control unit 6 performs the sixth to eighth modes as shown in Table 1. Repeat the switching action. Here, the control unit 6 balances the discharge and charge of the first capacitor C1 and the second capacitor C2 by adjusting the time length in the sixth mode and the seventh mode.

  In the present embodiment, the control unit 6 switches the first to eighth modes while changing the duty ratio of the PWM signal, so that the waveform of the final output voltage approximates a sine wave. The output voltage generated between the output point 103 and the second output point 104 is controlled. In short, the power conversion device 1 changes the magnitude of the output voltage generated between the first output point 103 and the second output point 104 in five stages by the control unit 6, thereby changing the sinusoidal AC voltage to the first voltage. Occurs between the third output point 105 and the fourth output point 106.

  The fourth mode and the fifth mode are both modes in which the output voltage is 0 [V] and do not contribute to the discharging and charging of the first capacitor C1 and the second capacitor C2. For this reason, it may be possible to omit either the fourth mode or the fifth mode. However, considering the positive / negative balance of the final output voltage, the power conversion device 1 is configured as the fourth mode. By dividing the fifth mode, the switching loss can be reduced and the efficiency is improved.

  According to the power conversion device 1 of the present embodiment, the number of elements through which a current flows (hereinafter referred to as “the number of passing elements”) among the semiconductor elements (switching elements, diodes) In this mode, it is “4” or less.

  In particular, in the third and fourth modes in which the second bidirectional switch 14 is fully turned on, even if the eleventh switching element Q11 and the twelfth switching element Q12 are counted as separate elements, the number of passing elements is “ 4 ". Similarly, in the fifth and sixth modes in which the first bidirectional switch 13 is fully turned on, even if the ninth switching element Q9 and the tenth switching element Q10 are counted as separate elements, the number of passing elements is “4”. Therefore, when the first and second bidirectional switches 13 and 14 are each composed of one element, the number of passing elements in the third to sixth modes is “3”.

  Meanwhile, it is preferable that the control unit 6 determines whether to charge or discharge the first capacitor C1 and the second capacitor C2 according to the detection results of the first detection unit 21 and the second detection unit 22. In the present embodiment, the detection result of the first detection unit 21 (the voltage V1 of the first capacitor C1) and the detection result of the second detection unit 22 (the voltage V2 of the second capacitor C2) are output to the microcomputer 62. The microcomputer 62 obtains the average value Vc of the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 obtained individually as described above. The microcomputer 62 is configured to select whether to charge or discharge the capacitor according to the average value Vc. The average value Vc is expressed by Vc = (V1 + V2) / 2.

  More specifically, for example, in the periods T1 to T3 in which the final output voltage varies in the range of 0 [V] to E [V], the control unit 6 switches the first to fourth modes as shown in Table 1. The operation is repeated. In these cases (periods T1 to T3), the microcomputer 62 detects whether the second mode (charge mode) or the third mode (discharge mode) is selected by the first detection unit 21 and the second detection. This is determined according to the detection result of the unit 22. That is, the microcomputer 62 compares the average value Vc obtained from the detection results of the first detection unit 21 and the second detection unit 22 with the target voltage, and the second mode (charging mode) and the third mode are compared based on the comparison result. (Discharge mode) is selected. The microcomputer 62 selects the third mode that is the discharge mode if the average value Vc is larger than the target voltage, and selects the second mode that is the charge mode if the average value Vc is smaller than the target voltage. Here, the target voltage is a reference voltage (E / 4 [V]).

  Similarly, in the period T4 to T6 in which the final output voltage varies in the range of 0 [V] to -E [V], the control unit 6 performs the operation of switching the fifth to eighth modes as shown in Table 1. repeat. In these cases (periods T4 to T6), the microcomputer 62 determines whether the sixth mode (discharge mode) or the seventh mode (charge mode) is to be selected. This is determined according to the detection result of the unit 22. That is, the microcomputer 62 compares the average value Vc obtained from the detection results of the first detection unit 21 and the second detection unit 22 with the target voltage (E / 4 [V]), and the seventh mode ( Either a charging mode) or a sixth mode (discharging mode) is selected. If the average value Vc is larger than the target voltage, the microcomputer 62 selects the sixth mode that is the discharge mode, and if the average value Vc is smaller than the target voltage, the microcomputer 62 selects the seventh mode that is the charge mode.

  Thereby, the both-ends voltage of the 1st capacitor C1 and the both-ends voltage of the 2nd capacitor C2 at the time of basic operation are maintained at the reference voltage (E / 4 [V]) which is a target voltage, respectively. However, the operation of the control unit 6 described above is an operation in the case where the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 are balanced, and the voltage V1 and V2 are unbalanced (unbalanced). ) Will be described in the “One-sided discharge mode” column.

  Moreover, it is preferable that the control part 6 switches charge and discharge of a capacitor (1st capacitor C1 and 2nd capacitor C2) with a predetermined switching period. The switching period here is set in accordance with, for example, the period of the PWM signal.

  By the way, as described above, in the power conversion device 1 of the present embodiment, the second bidirectional switch 14 is fully turned on in the third and fourth modes, and the first bidirectional switch in the fifth and sixth modes. Reference numeral 13 denotes an all-on state. That is, in any of the first to eighth modes, the element through which the current flows among the semiconductor elements (switching elements, diodes) is any one of the first to twelfth switching elements Q1 to Q12, and No current flows through the twelve diodes D1 to D12). Therefore, the power conversion device 1 can flow a bidirectional current between the first output point 103 and the second output point 104 in any of the first to eighth modes.

  Hereinafter, the current flowing through the conversion circuit 10 in the direction indicated by the thick arrow in FIGS. 2A, 2B, 3A, 3B, 4A, 4B, 5A, and 5B is referred to as “forward current” and is converted in the opposite direction to the forward current. The current flowing through the circuit 10 is referred to as “reverse current”. That is, in the first to fourth modes in which the final output voltage varies in the range of 0 [V] to E [V], the current from the first output point 103 to the third output point 105 is the forward current. In the fifth to eighth modes in which the final output voltage varies in the range of 0 [V] to -E [V], the current from the second output point 104 to the fourth output point 106 is the forward current.

  In this way, the power conversion device 1 allows the output current to flow between the first output point 103 and the second output point 104, the first output point 103, and the first output point because the conversion circuit 10 supports bidirectional current. A phase difference can be set between the output voltage generated between the two output points 104. In short, if there is a phase difference between the output current and the output voltage, a period in which the output current is different from the output voltage (for example, the output voltage is positive and the output current is negative) occurs.

  Here, while the output current and the output voltage have the same sign, the current flowing through the conversion circuit 10 is a forward current, but when the output current and the output voltage have different signs, the current flows through the conversion circuit 10. The current is a reverse current. Therefore, when the power conversion device 1 sets a phase difference between the output current and the output voltage, the conversion circuit 10 needs to support a bidirectional current. In the power conversion device 1 of this embodiment, since the conversion circuit 10 supports bidirectional current, it is possible to set a phase difference between the output current and the output voltage.

  In particular, when the power conversion device 1 is used for the power conditioner 20 (see FIG. 7) for the solar power generation device, the power conversion device is used for the purpose of detecting the isolated operation and suppressing the voltage rise of the system power supply 7. 1 may set a phase difference between the output current and the output voltage. Moreover, when the power converter device 1 is used for the power conditioner for the power storage device, the power converter device 1 is configured to supply power by setting a phase difference between the output current and the output voltage. To switch between charging and discharging of the power storage device. The power conversion device 1 of the present embodiment can cope with such a use by creating a state in which bidirectional current can pass through the conversion circuit 10.

<Configuration of the inverter>
As shown in FIG. 7, the power conditioner 20 according to the present embodiment includes the power conversion device 1 and the disconnector 9. The disconnector 9 is electrically connected between the first output point 103 (see FIG. 1) and the second output point 104 (see FIG. 1) and the system power supply 7. In the example of FIG. 7, the disconnector 9 is electrically connected between the third output point 105 and the fourth output point 106 and the system power supply 7. In other words, the resolver 9 is connected to the first output point 103 and the second output point 104 via the filter circuit 5 (see FIG. 1). In other words, the circuit breaker 9 has only to be between the first output point 103 and the second output point 104 and the system power supply 7 and is directly connected to the first output point 103 and the second output point 104. Is not essential, and may be connected to the subsequent stage of the filter circuit 5 as in this embodiment.

  Here, the circuit breaker 9 is electrically connected between the first contact point 91 electrically connected between the third output point 105 and the system power supply 7, and between the fourth output point 106 and the system power supply 7. And a second contact portion 92 connected to the. However, the circuit breaker 9 only needs to be electrically connected between at least one of the third output point 105 and the fourth output point 106 and the system power supply 7, and the first contact part 91 and the second contact part 9 Any of 92 may be omitted.

  The power conditioner 20 performs grid connection operation in a steady state, converts DC power input from the DC power supply 100 into AC power by the power conversion device 1, and outputs the AC power to the system power supply 7 and the load 8. Although detailed description is omitted, the power conditioner 20 performs a self-sustained operation in which the disconnector 9 is opened and AC power is output in a state disconnected from the system power supply 7 in the event of an abnormality such as a power failure of the system power supply 7. It is configured as follows.

  According to the power conditioner 20, the first converter circuit 11 and the second converter circuit 12 and the system power supply 7 can be electrically disconnected by opening (disconnecting) the disconnector 9. Therefore, the power conditioner 20 opens the disconnector 9 during the start-up period after the power is turned on and before the power converter 1 starts the basic operation described above, so that the first output point 103 and the second output point are opened. A current path including the filter circuit 5 can be formed between the terminal 104 and the terminal 104.

  The current path here is a current path including the inductor L1, the third capacitor C3, and the inductor L2 constituting the filter circuit 5. By using this current path as a charging path, the power conversion device 1 uses the first capacitor C1 and the second capacitor even if the third output point 105 and the fourth output point 106 are electrically insulated. C2 can be charged.

  Therefore, the power conversion device 1 can charge the first capacitor C1 and the second capacitor C2 even if the third output point 105 and the fourth output point 106 are not connected to the system power supply 7. In other words, the power conversion device 1 operates in a steady state even when no load is connected between the pair of output terminals (the third output point 105 and the fourth output point 106) (no load state). Necessary capacitors (first capacitor C1 and second capacitor C2) can be charged. The steady operation here refers to the operation of the power conversion apparatus 1 after the start-up period has elapsed, that is, after the first capacitor C1 and the second capacitor C2 are charged to the reference voltage (E / 4 [V]). Therefore, it is synonymous with the basic operation described above.

<One-sided discharge mode>
8A, 8B, 9A, 9B will be described below with respect to the operation of the power converter 1 when an imbalance (unbalance) occurs between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2. This will be described in detail with reference to. In the drawing, a thick arrow represents a current path, and a switching element with a dotted circle represents an on-state element.

  In the present embodiment, the controller 6 controls the first to eighth modes so that the one-side discharge mode is set when the difference between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 exceeds a predetermined threshold. The switching elements Q1 to Q8 and the first and second bidirectional switches 13 and 14 are controlled. Here, the voltage V1 of the first capacitor C1 is detected by the first detector 21, and the voltage V2 of the second capacitor C2 is detected by the second detector 22.

  Specifically, for example, in the periods T1 to T3 in which the final output voltage fluctuates in the range of 0 [V] to E [V], the microcomputer 62 normally has the second mode (charging mode) and the third mode. (Discharge mode) is switched to maintain the voltages V1 and V2 at the specified voltage. In this state, if the difference between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 exceeds the threshold value V0, the microcomputer 62 replaces the third mode which is the normal discharge mode with the one-side discharge mode. Select.

  For example, when the voltage V1 of the first capacitor C1 is higher than the voltage V2 of the second capacitor C2 and the difference (V1−V2) between the two voltages V1 and V2 is larger than the threshold value V0, the microcomputer 62 The one-side discharge mode of FIG. 8A is selected so that only C1 is discharged. In the one-side discharge mode, as shown in FIG. 8A, the second switching element Q2 of the first conversion circuit 11, the sixth switching element Q6 of the second conversion circuit 12, and the eleventh of the second bidirectional switch 14 are used. , 12 are in the on state, respectively.

  In this state, the second output point 104 is connected to the first output point via the sixth switching element Q6, the eleventh switching element Q11, the twelfth switching element Q12, the first capacitor C1, and the second switching element Q2. 103 is electrically connected. Therefore, in the state of FIG. 8A, only the first capacitor C1 having a higher voltage among the first capacitor C1 and the second capacitor C2 is discharged, and the voltage V1 of the first capacitor C1 decreases. In this state, the potential at the first output point 103 is higher than the potential at the second output point 104 by the voltage across the first capacitor C1 (E / 4 [V]). And the output voltage of the power converter 1 generated between the first output point 104 and the second output point 104 is E / 4 [V].

  When the voltage V2 of the second capacitor C2 is higher than the voltage V1 of the first capacitor C1 and the difference (V2−V1) between the voltages V1 and V2 is larger than the threshold value V0, the microcomputer 62 The one-side discharge mode of FIG. 8B is selected so that only the capacitor C2 is discharged. In this one-side discharge mode, as shown in FIG. 8B, the third switching element Q3 of the first conversion circuit 11, the seventh switching element Q7 of the second conversion circuit 12, and the eleventh of the second bidirectional switch 14 , 12 are in the on state, respectively.

  In this state, the second output point 104 is connected to the first output point via the seventh switching element Q7, the second capacitor C2, the eleventh switching element Q11, the twelfth switching element Q12, and the third switching element Q3. 103 is electrically connected. Therefore, in the state of FIG. 8B, only the second capacitor C2 having a higher voltage among the first capacitor C1 and the second capacitor C2 is discharged, and the voltage V2 of the second capacitor C2 decreases. In this state, the potential at the first output point 103 is higher than the potential at the second output point 104 by the voltage across the second capacitor C2 (E / 4 [V]). And the output voltage of the power converter 1 generated between the first output point 104 and the second output point 104 is E / 4 [V].

  On the other hand, in the period T4 to T6 in which the final output voltage varies in the range of 0 [V] to -E [V], the microcomputer 62 normally has the seventh mode (charge mode) and the sixth mode (discharge mode). ) To maintain the voltages V1 and V2 at the specified voltage. In this state, when the difference between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 exceeds the threshold value V0, the microcomputer 62 replaces the sixth mode which is the normal discharge mode with the one-side discharge mode. Select.

  For example, when the voltage V1 of the first capacitor C1 is higher than the voltage V2 of the second capacitor C2 and the difference (V1−V2) between the two voltages V1 and V2 is larger than the threshold value V0, the microcomputer 62 The one-side discharge mode of FIG. 9A is selected so that only C1 is discharged. In this one-side discharge mode, as shown in FIG. 9A, the third switching element Q3 of the first conversion circuit 11, the seventh switching element Q7 of the second conversion circuit 12, and the ninth switching element Q7 of the first bidirectional switch 13 are arranged. , 10 switching elements Q9, Q10 are in the ON state.

  In this state, the first output point 103 is connected to the second output point via the third switching element Q3, the first capacitor C1, the ninth switching element Q9, the tenth switching element Q10, and the seventh switching element Q7. 104 is electrically connected. Therefore, in the state of FIG. 9A, only the first capacitor C1 having a higher voltage among the first capacitor C1 and the second capacitor C2 is discharged, and the voltage V1 of the first capacitor C1 decreases. In this state, the potential at the first output point 103 is lower than the potential at the second output point 104 by the voltage across the first capacitor C1 (E / 4 [V]). And the output voltage of the power converter 1 generated between the first output point 104 and the second output point 104 is −E / 4 [V].

  When the voltage V2 of the second capacitor C2 is higher than the voltage V1 of the first capacitor C1 and the difference (V2−V1) between the voltages V1 and V2 is larger than the threshold value V0, the microcomputer 62 The one-side discharge mode of FIG. 9B is selected so that only the capacitor C2 is discharged. In this one-side discharge mode, as shown in FIG. 9B, the second switching element Q2 of the first conversion circuit 11, the sixth switching element Q6 of the second conversion circuit 12, and the ninth switching element Q1 of the first bidirectional switch 13 are used. , 10 switching elements Q9, Q10 are in the ON state.

  In this state, the first output point 103 is connected to the second output point via the second switching element Q2, the ninth switching element Q9, the tenth switching element Q10, the second capacitor C2, and the sixth switching element Q6. 104 is electrically connected. Therefore, in the state of FIG. 9B, only the second capacitor C2 having a higher voltage among the first capacitor C1 and the second capacitor C2 is discharged, and the voltage V2 of the second capacitor C2 decreases. In this state, the potential at the first output point 103 is lower than the potential at the second output point 104 by the voltage across the second capacitor C2 (E / 4 [V]). And the output voltage of the power converter 1 generated between the first output point 104 and the second output point 104 is −E / 4 [V].

  The conversion circuit 10 operates in the one-side discharge mode as described above, whereby only the capacitor having the higher voltage of the first capacitor C1 and the second capacitor C2 is discharged. Therefore, the conversion circuit 10 repeats the above-described one-side discharge mode one or more times, thereby reducing the difference (V2−V1) between the voltage V2 of the second capacitor C2 and the voltage V1 of the first capacitor C1, and the threshold value V0. It will fit below. As a result, the power conversion device 1 can balance the voltages of the pair of capacitors even when the voltage imbalance (unbalance) of the pair of capacitors (the first capacitor C1 and the second capacitor C2) occurs. is there.

  The control unit 6 of the present embodiment described above operates according to the flowchart shown in FIG. 10, for example.

  First, the control unit 6 compares the average value Vc of the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 with the reference voltage (E / 4 [V]) (S1). At this time, if the average value Vc is equal to or higher than the reference voltage (S1: Yes), the control unit 6 obtains a difference value (V2−V1) obtained by subtracting the voltage V1 of the first capacitor C1 from the voltage V2 of the second capacitor C2. The threshold value V0 is compared (S2). If the difference value (V2-V1) is equal to or less than the threshold value V0 (S2: Yes), the control unit 6 subtracts the voltage V2 of the second capacitor C2 from the voltage V1 of the first capacitor C1 (V1-V2). And the threshold value V0 are compared (S3). If the difference value (V1-V2) is equal to or less than the threshold value V0 (S3: Yes), the control unit 6 outputs a discharge command to discharge both the first capacitor C1 and the second capacitor C2. A mode (third mode or sixth mode) is selected (S4). That is, if the voltages V1 and V2 are in a balanced state, the control unit 6 selects a normal discharge mode.

  On the other hand, if the difference value (V1−V2) exceeds the threshold value V0 in process S3 (S3: No), the control unit 6 selects a one-side discharge mode in which only the first capacitor C1 having a high voltage is discharged ( S5). If the difference value (V2−V1) exceeds the threshold value V0 in process S2 (S2: No), the control unit 6 selects a one-side discharge mode in which only the second capacitor C2 having a high voltage is discharged ( S6).

  On the other hand, if the average value Vc is less than the reference voltage (S1: No), the control unit 6 outputs a charge command and charges the first capacitor C1 and the second capacitor C2 in a normal charging mode ( The second mode or the seventh mode is selected (S7).

  The control unit 6 repeats the processes of S1 to S7, and balances the voltages V1 and V2 while maintaining the voltages of the first capacitor C1 and the second capacitor C2 at the reference voltage.

<Effect>
The power conversion device 1 of the present embodiment described above has the first capacitor C1 and the second capacitor C2 when the difference between the voltage V1 of the first capacitor C1 and the voltage V2 of the second capacitor C2 exceeds a predetermined threshold. In this mode, only the capacitor having the higher voltage is discharged. In other words, the power conversion device 1 discharges only the capacitor with the higher voltage even when the voltage imbalance (imbalance) of the pair of capacitors (the first capacitor C1 and the second capacitor C2) occurs. It is possible to balance the voltage of the capacitors. Therefore, the power conversion device 1 of this embodiment has an advantage that the withstand voltage required for the capacitor can be lowered by balancing the voltages of the pair of capacitors.

  In short, in the conventional power conversion device, when the voltage imbalance of a pair of capacitors occurs, the voltage of one capacitor may greatly exceed the specified voltage. Therefore, it is necessary to use a high voltage capacitor. On the other hand, the power conversion device 1 of the present embodiment can suppress the voltage of one capacitor from greatly exceeding the specified voltage by balancing the voltages of the pair of capacitors, and as a result, A relatively low withstand voltage capacitor can be used as the capacitor. Therefore, the power conversion device 1 of the present embodiment can reduce the size of the pair of capacitors.

  Moreover, the power conversion device 1 balances the voltages of the pair of capacitors by discharging one of the capacitors when the voltage imbalance of the pair of capacitors occurs. That is, since the power conversion device 1 is configured to discharge instead of charging only one capacitor, when the voltage imbalance occurs, the first capacitor C1 and the second capacitor C2 are supplied from the DC power supply 100. Operates in an electrically disconnected state. Therefore, the power conversion device 1 can prevent the occurrence of leakage current due to the voltage imbalance of the pair of capacitors.

  Further, in the power conversion device 1, as in the present embodiment, the conversion circuit 10 includes a first conversion circuit 11 and a second conversion circuit 12, a first bidirectional switch 13 and a second bidirectional switch 14. It is preferable to provide. The power conversion device 1 includes a first conversion circuit 11 and a second conversion circuit 12 that are connected in parallel between both ends of a DC power supply 100, and the first conversion circuit 11 is connected between the first conversion circuit 11 and the second conversion circuit 12. The bidirectional switch 13 and the second bidirectional switch 14 are connected. Here, the first conversion circuit 11 includes four switching elements (first to fourth switching elements Q1 to Q4) and one capacitor (first capacitor C1). Similarly, the second conversion circuit 12 includes four switching elements (fifth to eighth switching elements Q5 to Q8) and one capacitor (second capacitor C2).

  In this configuration, the current input from the DC power supply 100 to the power conversion device 1 is out of ten switching elements (first to eighth switching elements Q1 to Q8 and first and second bidirectional switches 13 and 14). It passes through at most four elements. Therefore, this power conversion device 1 has the advantage that the sum of the conduction loss (loss) of the switching elements is relatively small, and the power conversion efficiency can be further improved.

  Further, the power conversion device 1 generally requires a large heat radiating device (an air cooling device such as a heat sink or a fan) because the calorific value increases as the conduction loss increases. The power conversion device 1 of the present embodiment can be expected to reduce the size of the heat dissipation device by suppressing conduction loss.

  Compared with the configuration described in Patent Document 1, the power conversion device 1 of the present embodiment also has an advantage that the entire device can be reduced in size by the amount that does not require a voltage dividing capacitor. In other words, the power conversion device described in Patent Document 1 divides the DC voltage E by E / 2 by applying the DC voltage E to a series circuit of two DC capacitors. The capacitor is an essential configuration. On the other hand, since the power conversion device 1 of the present embodiment does not require a voltage dividing capacitor, the entire device can be reduced in size accordingly.

  In this case, as in this embodiment, a voltage that is 1/4 of the voltage applied between the first input point 101 and the second input point 102 from the DC power supply 100 is used as the reference voltage. Is preferred. In this case, the control unit 6 controls the first to eighth switching elements Q1 to Q8 and the first and second switching elements so that the first capacitor C1 and the second capacitor C2 repeat charging and discharging around the reference voltage, respectively. It is preferable to control the bidirectional switches 13 and 14.

  According to this configuration, the power conversion device 1 uses the output voltage generated between the first output point 103 and the second output point 104 as E [V], E / in the first to fourth modes as described above. It can be switched in three stages of 2 [V] and 0 [V]. In the fifth to eighth modes, the power conversion device 1 sets the output voltage generated between the first output point 103 and the second output point 104 to 0 [V], −E / 2 [V], −E. Switching is performed in three stages [V]. As a result, the power conversion apparatus 1 switches the first to eighth modes to change the output voltage to E [V], E / 2 [V], 0 [V], −E / 2 [V], − It can be switched in 5 stages of E [V].

  In short, the power conversion device 1 according to the present embodiment is a 5-level inverter that switches the output voltage in 5 stages, but the operation is the same as that of the 3-level inverter, so the number of passing elements is the same as that of the 3-level inverter. “4” or less. Therefore, this power conversion device 1 can suppress the number of passing elements to be smaller than the number of passing elements “6” of a general five-level inverter, and as a result, can further improve the power conversion efficiency. .

  Further, as in the present embodiment, the power conversion apparatus 1 further includes a first detection unit 21 that detects the voltage V1 of the first capacitor C1 and a second detection unit 22 that detects the voltage V2 of the second capacitor C2. It is preferable to provide. In this case, the control unit 6 performs charging of the first capacitor C1 and the second capacitor C2 such that the average value Vc of the detection result of the first detection unit 21 and the detection result of the second detection unit 22 becomes the reference voltage. It is preferable to switch between discharge. Furthermore, in this case, when the difference between the detection result of the first detection unit 21 and the detection result of the second detection unit 22 exceeds the threshold value V0, the control unit 6 causes the first to eighth operations to be in the one-side discharge mode. The switching elements Q1 to Q8 and the first and second bidirectional switches 13 and 14 are preferably controlled. Here, the one-side discharge mode is a mode in which only the capacitor having the higher voltage out of the first capacitor C1 and the second capacitor C2 is discharged.

  According to this configuration, the control unit 6 uses both the voltages V1 and V2 as reference voltages based on the detection result (voltage V1) of the first detection unit 21 and the detection result (voltage V2) of the second detection unit 22. While maintaining, the difference between the two voltages V1 and V2 can be suppressed to the threshold value V0 or less. Therefore, the power conversion device 1 has a control for maintaining both the voltages V1 and V2 at the reference voltage and a control for suppressing the difference between the voltages V1 and V2 to be equal to or less than the threshold value V0 as compared to the case of using separate detection units. Thus, the required number of detection units can be suppressed.

  Further, as in the present embodiment, the controller 6 discharges only the first capacitor C1 out of the first capacitor C1 and the second capacitor C2, and the second and sixth switching elements Q2, Q6 and the second capacitor It is preferable to turn on the combination of the two bidirectional switches 14. Alternatively, when the control unit 6 discharges only the first capacitor C1 out of the first capacitor C1 and the second capacitor C2, the control unit 6 selects a combination of the third and seventh switching elements Q3 and Q7 and the first bidirectional switch 13. You may turn it on. Further, when discharging only the second capacitor C2 out of the first capacitor C1 and the second capacitor C2, the controller 6 controls the third and seventh switching elements Q3, Q7 and the second bidirectional switch 14. Preferably the combination is turned on. Alternatively, when the control unit 6 discharges only the second capacitor C2 out of the first capacitor C1 and the second capacitor C2, the control unit 6 selects a combination of the second and sixth switching elements Q2 and Q6 and the first bidirectional switch 13. You may turn it on.

  According to this configuration, even in the one-side discharge mode in which only one capacitor is discharged, at most four of the first to twelfth switching elements Q1 to Q12 are input to the power conversion device 1 from the DC power source 100. It just passes through the elements. Therefore, this power conversion device 1 has the advantage that the sum of the conduction loss (loss) of the switching elements is relatively small, and the power conversion efficiency can be further improved.

  Further, according to the power conditioner 20 according to the present embodiment, the disconnector 9 is opened (disconnected), thereby electrically connecting the first conversion circuit 11 and the second conversion circuit 12 to the system power supply 7. Can be separated. Therefore, the power conditioner 20 performs grid connection operation in a steady state, and when the system power supply 7 is abnormal, such as a power failure, opens the disconnector 9 and outputs AC power in a state disconnected from the system power supply 7. You can perform autonomous operation.

  Further, as in the present embodiment, the operating state of the first bidirectional switch 13 is such that the current flowing from the second connection point 202 to the first connection point 201 is cut off, and the first connection point 201 to the second connection point. It is preferable to further include a half-on state in which the current flowing to 202 is passed. In this case, the operating state of the second bidirectional switch 14 blocks the current flowing from the third connection point 203 to the fourth connection point 204 and passes the current flowing from the fourth connection point 204 to the third connection point 203. It is preferable to further include a half-on state.

  According to this configuration, the first bidirectional switch 13 is half-on in a mode in which the current flowing from the first connection point 201 to the second connection point 202 does not need to be interrupted as in the seventh and eighth modes. The state is fine. Therefore, the control unit 6 can continue to turn on the tenth switching element Q10 in the period (period T4 to T6) in which the operation for switching the fifth to seventh modes or the sixth to eighth modes is repeated. In other words, in the fifth and sixth modes, the first bidirectional switch 13 is all on, so that the tenth switching element Q10 is turned off whenever the tenth switching element Q10 is turned off each time the mode is switched to the seventh and eighth modes. Switching loss may occur. The power converter 1 of the present embodiment allows the first bidirectional switch 13 to keep the tenth switching element Q10 on when the fifth to seventh modes or the sixth to eighth modes are switched. The generated switching loss can be reduced.

  Similarly, in the mode in which the current flowing from the fourth connection point 204 to the third connection point 203 does not need to be interrupted as in the first and second modes, the second bidirectional switch 14 may be in a half-on state. . Therefore, the power conversion device 1 of the present embodiment is configured so that the twelfth switching element Q12 is kept on when the first to third modes or the second to fourth modes are switched, so that the second bidirectional switch 14 can reduce the switching loss.

  Further, if the control unit 6 shifts the first bidirectional switch 13 from the half-on state to the fully-on state in a state where the current flows through the first bidirectional switch 13, the first bidirectional switch 13. Switching loss caused by the switch 13 can be further reduced. That is, for example, when switching from the seventh mode to the sixth mode, the control unit 6 turns on the ninth switching element Q9 while the ninth diode D9 is turned on, so that the ninth switching is performed. Zero volt switching of the element Q9 can be realized. Similarly, if the control unit 6 shifts the second bidirectional switch 14 from the half-on state to the fully-on state in a state where the current is flowing through the second bidirectional switch 14, Switching loss caused by the directional switch 14 can be further reduced.

  In the power conversion device 1, the conversion circuit 10 includes the first conversion circuit 11 and the second conversion circuit 12, the first bidirectional switch 13 and the second bidirectional switch 14 as described above. It is not limited and can be changed as appropriate. The number of switching elements is not limited to 12 of the first to twelfth switching elements Q1 to Q12, and can be changed as appropriate.

  The first to eighth switching elements Q1 to Q8 and the ninth to twelfth switching elements Q9 to Q12 are not limited to depletion type n-channel MOSFETs, and other semiconductor switches may be used. For example, a power semiconductor device using a wide band gap semiconductor material such as IGBT (Insulated Gate Bipolar Transistor) or GaN (gallium nitride) is used.

  Also, the specific configuration of the bidirectional switch (each of the first bidirectional switch 13 and the second bidirectional switch 14) is not limited to the configuration described above. The bidirectional switch may be a double gate (dual gate) structure bidirectional switch using a wide band gap semiconductor material such as GaN (gallium nitride).

DESCRIPTION OF SYMBOLS 1 Power converter 11 1st conversion circuit 12 2nd conversion circuit 13 1st bidirectional switch 14 2nd bidirectional switch 21 1st detection part 22 2nd detection part 6 Control part 7 System power supply 9 Separator 20 Power Conditioner 100 DC power supply 101 First input point 102 Second input point 103 First output point 104 Second output point 201 First connection point 202 Second connection point 203 Third connection point 204 Fourth connection point C1 First capacitor C2 Second capacitor Q1 to Q8 First to eighth switching elements V1 First capacitor voltage V2 Second capacitor voltage

Claims (5)

A first conversion circuit and a second conversion circuit electrically connected in parallel between a first input point on the high potential side of the DC power supply and a second input point on the low potential side of the DC power supply. Prepared,
The first conversion circuit includes a first switching element, a second switching element, a third switching element, a fourth switching element from the first input point side between the first input point and the second input point. First to fourth switching elements electrically connected in series in the order of the switching elements, and a second circuit electrically connected in parallel to the series circuit of the second switching element and the third switching element. 1 capacitor, and a connection point between the second switching element and the third switching element is a first output point,
The second conversion circuit includes a fifth switching element, a sixth switching element, a seventh switching element, an eighth switching element from the first input point side between the first input point and the second input point. In the order of the switching elements, the fifth to eighth switching elements electrically connected in series, and the sixth switching element and the seventh switching element connected in parallel with the series circuit. A second output point is a connection point between the sixth switching element and the seventh switching element,
Electrical connection between a first connection point that is a connection point of the first switching element and the second switching element and a second connection point that is a connection point of the seventh switching element and the eighth switching element. A first bidirectional switch connected electrically,
Electricity is provided between a third connection point that is a connection point of the third switching element and the fourth switching element and a fourth connection point that is a connection point of the fifth switching element and the sixth switching element. A second bidirectionally connected switch;
By controlling the first to eighth switching elements and the first and second bidirectional switches, the DC power source, the first capacitor, and the second capacitor for the first output point and the second output point, And a controller that changes the magnitude of the output voltage generated between the first output point and the second output point in a plurality of stages.
When the difference between the voltage of the first capacitor and the voltage of the second capacitor exceeds a predetermined threshold, only the capacitor having the higher voltage of the first capacitor and the second capacitor is controlled by the control unit. The first to eighth switching elements and the first and second bidirectional switches are controlled so as to be discharged. A voltage having a size that is 1/4 of a voltage applied between the first input point and the second input point from the DC power supply as a reference voltage,
The control unit includes the first to eighth switching elements and the first and second bidirectional switches so that the first capacitor and the second capacitor repeat charging and discharging around the reference voltage, respectively. It controls. The power converter device of Claim 1 characterized by the above-mentioned. A first detector for detecting a voltage of the first capacitor;
A second detector for detecting a voltage of the second capacitor;
The control unit charges and discharges the first capacitor and the second capacitor so that an average value of a detection result of the first detection unit and a detection result of the second detection unit becomes the reference voltage. switching,
When the difference between the detection result of the first detection unit and the detection result of the second detection unit exceeds the threshold value, the control unit has a higher voltage of the first capacitor and the second capacitor. The power conversion device according to claim 2, wherein the first to eighth switching elements and the first and second bidirectional switches are controlled such that only the first and second switching elements are discharged. The controller is
When discharging only the first capacitor of the first capacitor and the second capacitor, a combination of the second and sixth switching elements and the second bidirectional switch, or the third and seventh switches Turning on the combination of the switching element and the first bidirectional switch;
When discharging only the second capacitor of the first capacitor and the second capacitor, a combination of the third and seventh switching elements and the second bidirectional switch, or the second and sixth switches The power converter according to any one of claims 1 to 3, wherein a combination of a switching element and the first bidirectional switch is turned on. The power conversion device according to any one of claims 1 to 4,
A power conditioner comprising: a disconnector electrically connected between the first output point and the second output point and a system power supply.

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